Quantitative echosounders operating at multiple frequencies (e.g., 18, 38, 70, 120, 200, 333, and 710&#x2009;kHz) are often used to observe fish and zooplankton and identify their species. At frequencies above 100&#x2009;kHz, the absorption attenuation increases rapidly and decreases the signal-to-noise ratio (SNR). Also, incomplete compensation for the attenuation may result in measurement error. This paper addresses the effects of the attenuation and noise on high frequency measurements of acoustic backscatter from fish. It is shown that measurements of a fish with target strength of &#x2212;40&#x2009;dB at 200&#x2009;m depth are limited by SNR to frequencies up to about 100&#x2009;kHz. Above 100&#x2009;kHz, absorption coefficients must be matched to local environmental conditions.

Masahiko Furusawa

Effects of Noise and Absorption on High Frequency Measurements of Acoustic-Backscatter from Fish

Spatial distribution of selected metals (Al, Fe, Mn, Zn, Cu, and Co) in surface sediments in the EEZ of the east coast of Peninsular Malaysia was investigated. The aim of this paper is to determine the distribution pattern and pollution status of heavy metals in tropical shelf sediments since limited information is available. Heavy metal concentrations ranged between 207.58 and 491.33&#x2009;&#xb5;g&#xB7;g&#x2212;1 for Mn, 36.13 and 125.93&#x2009;&#xb5;g&#xB7;g&#x2212;1 for Zn, 14.49 and 22.33&#x2009;&#xb5;g&#xB7;g&#x2212;1 for Cu, 2.00 and 11.12&#x2009;&#xb5;g&#xB7;g&#x2212;1 for Co, 6.20 and 8.95&#x25; for Fe, and 0.94 and 6.62&#x25; for Al. The mean concentrations of heavy metals are in decreasing order as follows: Fe &#x3e; Al &#x3e; Mn &#x3e; Zn &#x3e; Cu &#x3e; Co. Most metals registered low concentrations at the nearshore areas. Pearson correlation indicates that most of the metals are derived from the miscellaneous sources. Based on the EFs and Igeo, it is implied that the surface sediment trace metal levels in the study area might be enriched by anthropogenic sources. However, the PLI suggests that this area is not contaminated from the measured heavy metals. This work is important to register the current levels of metals so that any change in concentration can be monitored and managed.

Hasrizal Shaari

Siti Nurul Hidayu Mohamad Azmi

Khawar Sultan

Joseph Bidai

Yuzwan Mohamad

Spatial Distribution of Selected Heavy Metals in Surface Sediments of the EEZ of the East Coast of Peninsular Malaysia

Ctenophores exist throughout the Northeast U.S. Continental Shelf Ecosystem, but the underlying mechanisms that control ctenophore populations at this scale are not clear. Ctenophore population data over the last 30 years coincides with changes in several water masses on the shelf, but discovering which water mass was most influential was problematic without mechanistic clarity. This paper strives to identify the relationship between oceanography and ctenophore populations over the last 30 years. Using a numerical modeling approach, we found a strong relationship between the North Atlantic Oscillation index, percent Labrador Subarctic Slope Water, and ctenophore population. We suggest these results might inform future efforts to develop a predictive capability for major changes in ctenophore population.

Rebecca Sparks

Michael Ford

David Abrahamson

Relating Ctenophore Population to Water Mass Indices in the Northeast U.S. Continental Shelf Ecosystem

The extent to which wind-driven seasonal upwelling cycles manifest in surface ocean temperature and nutrient variability along a monitoring line in the Southern Benguela upwelling system was investigated. Monitoring conducted monthly over a six-year period shows that surface temperature and nutrient concentrations exhibit very poor seasonality and weak correlation with the upwelling index. This is, despite clear evidence for spatial inshore-offshore gradients in temperature, nutrients, and chlorophyll, consistent with an upwelling regime. The upper ocean temperature gradient shows a much better correspondence to the upwelling index but at the same time demonstrates that surface heating, and not vertical mixing related to upwelling, controls the upper ocean temperature gradient. The results suggest that remote sensing techniques would be inadequate tools  to monitor upwelling events in the Southern Benguela. Also, the incidence of phytoplankton blooms is more likely triggered by stratified conditions associated with surface heating than relaxation of upwelling winds.

Hassan Ebrahiem Ismail

Johannes Jacobus Agenbag

Stephanie de Villiers

Bhekumusa Jabulani Ximba

Relation between Upwelling Intensity and the Variability of Physical and Chemical Parameters in the Southern Benguela Upwelling System

The knowledge of wind stress variability could represent an important contribution to understand the variability over upper layer ocean volume transports. The South Brazilian Bight (SBB) circulation had been studied by numerous researchers who predominantly attempted to estimate its meridional volume transport. The main objective and contribution of this study is to identify and quantify possible interannual variability in the ocean volume transport in the SBB induced by the sea surface wind stress field. A low resolution ocean global circulation model was implemented to investigate the volume transport variability. The results obtained indicate the occurrence of interannual variability in meridional ocean volume transports along three different zonal sections. These results also indicate the influence of a wind driven large-scale atmospheric process that alters locally the SBB and near-offshore region wind stress field and consequently causes interannual variability in the upper layer ocean volume transports. A strengthening of the southward flow in 25&#xb0;S and 30&#xb0;S was observed. The deep layer ocean volume transport in the three monitored sections indicates a potential dominance of other remote ocean processes. A small time lag between the integrated meridional volume transports changes in each monitored zonal section was observed.

Luiz Paulo de Freitas Assad

Carina Stefoni B&#xf6;ck

Rogerio Neder Candella

Luiz Landau

Influence of El Ni&#xf1;o Wind Stress Anomalies on South Brazil Bight Ocean Volume Transports

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International Journal of Oceanography